The present invention relates to technology suitably applied to a detection circuit that is used in wireless communication systems such as cellular phones and detects power of transmission output, and more particularly to technology suitably applied to an output power detection circuit in a wireless communication system that controls output power so as not to exceed specified maximum transmission power.
Generally, a transmission output part in wireless communication devices (mobile communication devices) such as cellular phones is provided with a radio frequency power amplifier circuit that amplifies a modulated transmission signal. In the wireless communication devices, control is performed so that desired transmission power is obtained by control signals from a baseband circuit or a control circuit of a microprocessor or the like.
In wireless communication devices of the GSM (Global System for Mobile Communication) system, such transmission power control is performed by providing an APC circuit and applying a feedback to a radio frequency power amplifier. The APC circuit generates a control signal for controlling the gain of the radio frequency power amplifier by detecting output power from the radio frequency power amplifier and comparing an output level indication signal Vramp from a control circuit such as a baseband circuit and detection output from an output power detection circuit (see Japanese Unexamined Patent Publication 2000-151310).
On the other hand, in wireless communication devices of the CDMA (Code Division Multiple Access) system, limiter control is performed which controls transmission power by detecting output power of a radio frequency power amplifier and outputting a limit signal from a control circuit such as a baseband circuit so as not to exceed maximum transmission power. Generally, conventional wireless communication devices of the CDMA often perform transmission control by controlling the gain of a variable gain amplifier within a transmitting circuit (RF-IC) for modulation and up-conversion that while keeping the gain of a radio frequency power amplifier constant, generates an input signal of the radio frequency power amplifier. Also in such wireless communication devices of the CDMA system, a detection circuit is required which detects the power of transmission output to perform the above-mentioned limiter control.